JP4455833B2 - Wafer polishing method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a polishing method for polishing a wafer such as silicon in which particles (defects) resulting from polishing do not occur.
[0002]
[Related technologies]
Conventionally, a method for producing a silicon wafer used as a semiconductor substrate material for a memory device or the like is generally a single crystal ingot using a Czochralski (CZ) method, a floating zone (FZ) method or the like. A single crystal growth step for manufacturing the wafer, a wafer manufacturing (processing) step in which the single crystal ingot is sliced and at least one main surface is processed into a mirror surface, and a device manufacturing step for forming a device on the mirror-polished wafer .
[0003]
The wafer manufacturing (processing) process will be described in more detail. A slicing process for slicing a single crystal ingot to obtain a thin disk-shaped wafer, and its outer periphery to prevent cracking and chipping of the wafer obtained by the slicing process. A chamfering process for chamfering a portion, a lapping process for flattening the wafer, an etching process for removing processing distortion remaining on the chamfered and lapped wafer, and a polishing (polishing) process for mirror polishing the wafer surface; It has a cleaning step of cleaning the polished wafer and removing the abrasive and foreign matter adhering to the wafer. The wafer processing step is a main step, and other processes such as a heat treatment process are added, the same process is performed in multiple stages, and the order of processes is changed.
[0004]
In particular, the polishing process is divided into a primary polishing process called rough polishing and a final polishing process called precision polishing. In some cases, the primary polishing process is further divided into two or more processes, and the primary and secondary polishing processes. And so on.
[0005]
In the polishing step, the polishing cloth rotating on the surface plate and the etched silicon wafer supported on the wafer support plate of the polishing head are brought into contact with each other with an appropriate pressure for polishing. At this time, an alkaline solution (referred to as a slurry or an abrasive) containing colloidal silica is used. By adding such a slurry to the contact surface between the polishing cloth and the silicon wafer, the slurry and the silicon wafer cause a mechanochemical action and the polishing proceeds.
[0006]
Various types of polishing apparatuses are used. For example, as shown in FIG. 3, there is a batch type that performs polishing while holding a plurality of wafers on one polishing head. In FIG. 3, the polishing apparatus A has a polishing surface plate 30 that is rotated by a rotating shaft 37 at a predetermined rotation speed. A polishing cloth P is stuck on the upper surface of the polishing surface plate 30.
[0007]
Reference numeral 33 denotes a work holding plate which is rotated by a rotating shaft 38 via an upper load 35 and is swung by a swinging means. A plurality of wafers W are pressed against the surface of the polishing pad P while being held on the lower surface of the work holding plate 33 by means of adhesion, and at the same time, a predetermined flow rate is passed through a slurry supply pipe 34 from a slurry supply device (not shown). Then, the slurry 39 is supplied onto the polishing pad P, and the surface to be polished of the wafer W is rubbed against the surface of the polishing pad P through the slurry 39 to polish the wafer W.
[0008]
In addition, there is a sheet-type polishing apparatus that holds and polishes one wafer on one polishing head. Also, there are various ways of holding the wafer, such as holding by vacuum suction, sticking to a work holding board with wax, sticking using the surface tension of water or the like. These are polishing apparatuses that polish one side, but there are also polishing apparatuses that simultaneously polish both sides.
[0009]
[Problems to be solved by the invention]
A foreign substance called particles may be observed on the surface of the wafer that has been polished in such a polishing step to have a flat and mirror polished wafer. The particles on the wafer are mainly classified into particles caused by crystals and particles caused by processing. Particles resulting from processing are classified into fine foreign matters that can be removed by cleaning and scratches and defects that cannot be removed. It is considered that particles caused by processing are mainly generated in the polishing step (caused by polishing).
[0010]
Accordingly, an object of the present invention is to provide a wafer polishing method in which defects (particles) are not generated due to such processing, particularly polishing.
[0011]
[Means for Solving the Problems]
As a result of intensive investigations by the present inventors, it has become clear that slurry (abrasive) is the cause of the generation of particles caused by this polishing. In particular, Na for pH adjustment used conventionally. ₂ CO _Three When excessive is added, such particles may be generated. This is because the silica used as the main component of the abrasive is Na ₂ CO _Three It is considered that the micro-aggregation is caused by excessive addition of the resin to form a gel-like lump and adversely affect the wafer surface.
[0012]
Therefore, the wafer polishing method of the present invention holds the wafer on a rotatable wafer holding plate, supplies slurry to the polishing cloth affixed to the rotatable surface plate, and makes the wafer and the polishing cloth slide. In the method for polishing a wafer surface, the slurry is an alkaline solution containing silica as a main component, and Na ₂ CO ₃ And a pH adjuster composed of at least one of NaOH, and manage the total amount of the pH adjuster added. Then, when the total amount of the pH adjusting agent reaches a predetermined value, the old slurry is discarded and a new slurry is prepared. Polishing in the state where the gel-like substance present in the slurry is controlled to 2.0% by weight or less with respect to the total amount of slurry and the electrical conductivity of the slurry is 13000 μS / cm or less, respectively, and the pH of the slurry is 10 to 13 It is characterized by doing.
[0013]
Conventionally, only the pH value of the slurry is regarded as important, and a pH adjusting agent is appropriately added to the slurry so that the pH of the slurry is adjusted to an arbitrary value, and the pH adjustment actually added to the slurry is adjusted. The amount of agent was not carefully controlled. Moreover, the gel-like substance in the slurry was not managed. In the present invention, by controlling the amount of the pH adjuster added in the slurry, the amount of the gel-like substance in the slurry is indirectly managed, and the particles caused by polishing, for example, the next-generation design rules are problematic. It is possible to reduce the possible particles of 0.065 μm or more.
[0014]
Further, in the wafer polishing method of the present invention, the electrical conductivity of the slurry is controlled to 13000 μS / cm or less for polishing. Is preferred . Even with such a configuration, the amount of the gel-like substance in the slurry can be indirectly controlled, and polishing can be performed in a state where particles resulting from polishing are reduced.
[0015]
Of course, you may manage the gel-like substance which exists in a slurry directly. But in that case, as mentioned above, Polishing by controlling the gel-like substance present in the slurry to 2.0% by weight or less based on the total amount of the slurry. Can also .
[0016]
The slurry used in the polishing method of the present invention is an alkaline solution mainly composed of silica, for example, when polishing a semiconductor substrate such as a silicon wafer. ₂ CO _Three And / or containing a pH adjusting agent comprising NaOH. In particular, polishing is preferably performed with an average primary particle size of silica in the slurry in a dispersed state (average particle size of silica in the slurry stock solution) of 5 nm to 30 nm and a silica concentration of 2 wt% to 20 wt% in the slurry. If such an abrasive | polishing agent is used, the wafer of a favorable mirror surface state will be obtained. At this time, it is preferable to polish the slurry (alkaline aqueous solution) at a pH of 10 to 13. Under such conditions, the polishing rate can be improved and a stable polishing rate can be obtained, and the abrasive cloth can be prevented from being clogged and the life of the polishing cloth can be improved.
[0017]
The polishing cloth to be used is not particularly limited, but a non-woven cloth type polishing cloth is preferable, and when the polishing is performed with a polishing margin of 0.5 μm or more and 2 μm or less, the effect is great. This is a polishing condition performed in an intermediate polishing step (secondary polishing) in polishing performed in a plurality of stages (for example, three stages of primary polishing, secondary polishing, and final polishing).
[0018]
The primary polishing has a larger polishing allowance to improve the flatness, and the final polishing has almost no polishing allowance (1 μm or less), and the main purpose is to improve the haze. Although it is considered that particles resulting from processing are generated even in the primary polishing, particles generated in the primary polishing can be removed by the secondary polishing under the same polishing conditions as the secondary polishing as described above. However, removal of particles caused by processing is difficult under polishing conditions that improve haze by finish polishing. It is necessary to prevent generation of particles before finish polishing or to remove particles before finish polishing. In the secondary polishing step, the polishing allowance is relatively large at 1 μm or more, the polishing conditions such as the polishing pressure are somewhat severe and the mechanical action is large, and defects are likely to occur due to the contact between the abrasive and the wafer. Therefore, the generation of particles can be effectively prevented by carrying out the wafer polishing method of the present invention in such a process.
[0019]
In the polishing method of the present invention, the slurry is preferably circulated and used. Recycling and use will lead to cost reduction. Note that the pH of the circulating slurry is controlled and Na ₂ CO _Three The pH is controlled to be kept constant by adding a pH adjuster comprising NaOH and / or NaOH. Especially Na ₂ CO _Three Is one of the causes of silica agglomeration, but it is easy to adjust pH and easy to handle in operation. In this way, when the slurry is used in a circulating manner, the addition amount of the pH adjusting agent in the slurry increases each time it is polished, so that the wafer is polished while managing the total amount of the pH adjusting agent in the slurry. The effect of carrying out a method of the present invention is great.
[0020]
The slurry is an alkaline solution mainly composed of silica and added with a pH adjusting agent. In addition, various additives such as tetramethylammonium hydroxide (TMAH), a chelating agent, an organic base and a salt thereof are added. It is also possible to adopt a configuration.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the accompanying drawings. However, the illustrated examples are illustrative only, and various modifications can be made without departing from the technical idea of the present invention. .
[0022]
FIG. 1 is a schematic side view illustrating an example of a polishing apparatus and a slurry supply / circulation system used in the polishing method of the present invention.
[0023]
In FIG. 1, the polishing apparatus A has the same configuration as that of the polishing apparatus shown in FIG. 3 described above, but the polishing apparatus A is provided with a slurry supply / circulation system as shown in FIG. Is different. That is, the polishing apparatus A has a polishing surface plate 30 that is rotated by a rotating shaft 37. A polishing cloth P is stuck on the upper surface of the polishing surface plate 30.
[0024]
Reference numeral 33 denotes a work holding plate which is rotated by a rotating shaft 38 via an upper load 35 and is swung by a swinging means. The plurality of wafers W are pressed against the surface of the polishing pad P while being held on the lower surface of the work holding plate 33, and simultaneously the slurry 39 is passed through the slurry supply pipe 34 from the slurry supply tank 50 of the slurry supply circulation system B. The surface to be polished of the wafer W is brought into sliding contact with the surface of the polishing pad P through the slurry 39, and the wafer W is polished.
[0025]
A slurry preparation tank 52 is installed above the slurry supply tank 50. The slurry preparation tank 52 is provided with a slurry stock solution feeding tube 54 for feeding a slurry stock solution, a pure water feeding tube 56 for feeding pure water, and a pH adjusting agent feeding tube 58 for feeding a pH adjusting agent, respectively. The slurry new liquid 39a can be prepared. Reference numeral 60 denotes a pH meter for measuring the pH of the new slurry 39a prepared in the slurry preparation tank 52, and the pH of the new slurry 39a is controlled.
[0026]
The slurry new liquid 39 a prepared in the slurry preparation tank 52 is supplied to the slurry supply tank 50 through the slurry new liquid supply pipe 62. On the other hand, the slurry 39 supplied to the polishing pad P through the slurry supply pipe 34 flows down while performing a polishing action and is recovered in a slurry recovery tank 64 provided below the surface plate 30. The recovered used slurry 39b is pumped and recovered by a pump 70 to a slurry supply tank 50 through a slurry recovery pipe 68 connected to a drain port 66 opened at the bottom of the slurry recovery tank 64. Reference numeral 72 denotes a pH adjusting agent supply pipe for supplying a pH adjusting agent to the slurry supply tank 50.
[0027]
Accordingly, the slurry supply tank 50 is supplied with the used slurry 39b, the slurry fresh solution 39a, and the pH adjuster, so that the polishing slurry 39 having a desired composition ratio can be produced. Reference numeral 74 denotes a pH meter for measuring the pH of the slurry 39 created in the slurry supply tank 50, and the pH of the slurry 39 is controlled. The amount of the pH adjusting agent added from the pH adjusting agent feeding pipe 58 and the pH adjusting agent supply pipe 72 is recorded by a flow meter (not shown) or the like, and the amount added is recorded from the beginning in the slurry stock solution. The total amount of the pH adjusting agent added to the slurry can be controlled including the amount of the added pH adjusting agent. Further, in the case of performing management based on electrical conductivity, an electrical conductivity meter (not shown) is installed in the slurry supply tank 50.
[0028]
By connecting the slurry supply / circulation system B having such a configuration to the polishing apparatus A, the used slurry 39b can be recovered and circulated for effective use of the slurry. When the slurry is circulated and used in this manner, depending on the amount of polishing waste (for example, polishing cloth waste), a filter or the like that removes the polishing waste is appropriately attached to the slurry collection pipe 68 or the slurry supply pipe 34 or the like. Install.
[0029]
The slurry (abrasive) used in the polishing method of the present invention is an alkaline solution composed of a solid component, various additives, and pure water.
[0030]
This solid component is silica having a substantially spherical shape, and the average primary particle diameter of silica in a dispersed state is about 5 to 30 nm. If the average particle diameter is less than the above, it is difficult to produce spherical silica, and the stability of the shape deteriorates. If it exceeds the above, the occurrence of defects increases, which is not preferable.
[0031]
This silica may be a silica fine powder, but it is preferable from the viewpoint of dispersion stability to use an aqueous colloidal silica (silica sol) liquid produced from water glass. Further, it is preferable that the aqueous colloidal silica liquid is alkaline because it can be easily adjusted to pH conditions as a polishing agent for silicon wafers. As such an alkaline colloidal silkworm, a commercially available product can be used.
[0032]
The silicon wafer abrasive of the present invention preferably has a pH adjusted to 10 to 13, and more preferably used in the range of pH 10 to 11 when the abrasive is used (polishing). If the pH is less than the above, the polishing cloth is likely to be clogged, and the polishing efficiency is poor, resulting in poor practicality. If the pH exceeds the above, the amount of the pH adjusting agent generally increases from the beginning. (Silica) is not preferred because it may agglomerate. The pH is adjusted by using any known alkaline agent (for example, NaOH, Na before use). ₂ CO _Three , KOH, ammonia, organic amine, etc.) can be used as additives. In addition, the abrasive used for polishing is repeatedly reused (circulated), and in such a case, Na is easy to control the pH. ₂ CO _Three Etc. are added to finely adjust the pH.
[0033]
The concentration of the solid component (silica) of the polishing agent (especially stock solution) for polishing the silicon wafer is not particularly limited, and the solid component (silica) concentration is 5 to 80% by weight, preferably 10 to 70% by weight. However, when this is used for polishing, it is diluted with pure water to make a slurry having a solid component concentration (silica concentration) of 2 to 20% by weight of the whole composition. What is necessary is just to set the density | concentration at the time of grinding | polishing suitably by the form of grinding | polishing apparatus, grinding | polishing conditions, etc.
[0034]
Furthermore, it is preferable that the polishing agent used in the polishing method of the present invention is added with a treatment or additive that does not aggregate the silica particles. Accordingly, for example, an organic base and a salt thereof can be added as various additives, and tetramethylammonium hydroxide (TMAH) or the like may be added in addition thereto. Furthermore, as an abrasive | polishing agent, the problem with respect to the improvement of a grinding | polishing speed | rate, metal contamination, etc. must be solved. Regarding such problems, a substance having a chelating effect, for example, sodium tripolyphosphate or other chelating agent may be further added to the abrasive to prevent metal contamination. Further, in order to improve the polishing rate, it is optional to add organic amine, piperazine or the like. Further, it is preferable that heavy metals and the like are sufficiently removed using an ion exchange resin or the like in the production stage of silica particles, and the concentration of Cu or Ni in the abrasive is preferably controlled to 1 ppb or less.
[0035]
The polishing cloth used in this polishing is not particularly limited, but is preferably a nonwoven cloth type polishing cloth. Polishing using a nonwoven fabric has a good polishing rate. In particular, when the present invention is implemented in a process of polishing using a polishing cloth having a hardness (Asker C hardness) of 50 or more, the effect is great. The cause of the occurrence of defects due to polishing is considered to be mainly due to the influence of the abrasive. However, since there are many defects due to polishing in the primary and secondary polishing using this type of polishing cloth, such polishing is performed. Compatibility with cloth is also considered as one of the causes of defects. With the polishing method of the present invention, it is possible to prevent the occurrence of defects due to polishing even if such a polishing cloth is used.
[0036]
【Example】
The present invention will be described more specifically with reference to the following examples. However, it is needless to say that these examples are shown by way of illustration and should not be construed in a limited manner.
[0037]
(Experimental Examples 1-6)
The result confirmed about the influence of the slurry (especially pH adjuster) with respect to the defect resulting from grinding | polishing is shown. First, the addition of a pH adjuster and the state change of the slurry were confirmed.
[0038]
As a solid component contained in the abrasive, silica sol having an average primary particle size of 20 nm obtained by ion exchange of water glass to obtain activated silicic acid and condensation polymerization by heating was used. The slurry stock solution containing such solid components is added to pure water and Na for pH adjustment. ₂ CO _Three Was added, and an experimental slurry S having a solid component (silica) concentration of about 3% by weight at pH 10.5 was prepared. It should be noted that NaOH is first added as a pH adjuster to the slurry stock solution used in this experimental example. Further, this experimental slurry S contains various additives.
[0039]
Using the experimental slurry S as described above, Na ₂ CO _Three Was added, and the state change of the experimental slurry S was confirmed. FIG. 2 is a schematic diagram showing the result of observing the state at that time. Actually, 70 ml of the above experimental slurry S is placed in the measuring cylinder M, and Na ₂ CO _Three Was added. The addition amount was 0 ml (Experiment 1), 1 ml (Experiment 2), 3 ml (Experiment 3), 5 ml (Experiment 4), 7 ml (Experiment 5), and 9 ml (Experiment 6).
[0040]
As shown in FIG. 2, Na ₂ CO _Three It can be seen that the gel-like white substance D precipitates as the amount of the addition increases (hereinafter this may be referred to as the gel-like substance D). Na ₂ CO _Three This gel-like precipitate D increases as the amount of added increases, indicating that the gel-like substance is composed mainly of Na. At this time, the amount of the pH adjusting agent in the slurry is the amount of NaOH added from the beginning and the added Na. ₂ CO _Three In the experimental example 1, about 0.28% by weight, in the experimental example 2, 0.81% by weight, in the experimental example 3, 1.31% by weight, in the experimental example 4, 1.78% by weight, and in the experimental example 5, 2 .22% by weight, which corresponds to 2.69% by weight in Experimental Example 6. Moreover, the amount of the precipitated gel substance D was also confirmed. In Experimental Example 1, about 0.08% by weight, 0.34% by weight in Experimental Example 2, 0.76% by weight in Experimental Example 3, 1.36% by weight in Experimental Example 4, based on the total weight of the abrasive. In Example 5, precipitation was 2.12% by weight, and in Experimental Example 6, precipitation was 3.05% by weight.
[0041]
(Polishing experiment example 1)
Since it became clear that such a precipitation arises, it confirmed about the influence which this gel-like deposit has on grinding | polishing. Polishing with the slurry used in Experimental Example 1 as a reference, so that the pH of a plurality of batches is constant (pH 10.5). ₂ CO _Three The pH adjuster was added and polishing was repeated. At this time, the addition amount of the pH adjusting agent was controlled.
[0042]
As a polishing apparatus, a general single-side polishing apparatus conventionally used as shown in FIG. 3 was used. When this apparatus was used to polish a plurality of batches of wafers, the number of particles caused by polishing began to increase rapidly in the 10th batch. Na until this time ₂ CO _Three As a result, it was 2.3% by weight based on the total amount of the slurry.
[0043]
From the previous experimental examples 1 to 6, it became clear that particles caused by polishing were likely to occur when the polishing conditions were the conditions of experimental example 5. Therefore, although the gel-like substance (precipitate) in the slurry is stirred in the tank, it is estimated that about 2.1% by weight is contained. From this result, it was also found that gel-like substances (precipitates) do not immediately lead to particles caused by polishing even if there is a certain amount.
[0044]
Depending on the commercially available slurry (abrasive), the same amount of Na as in the above-mentioned polishing experimental example 1 ₂ CO _Three In some cases, particles resulting from polishing are not observed and the amount of the gel-like substance is small. Depending on the difference in the stirring method and the components of the abrasive, NaOH or Na ₂ CO _Three It is considered that the gel-like substance (precipitate) is produced differently. As described above, Na or the like is used to remove Na. ₂ CO _Three Since the amount of the gelled material varies depending on the etc., the management of the pH adjuster is appropriately set depending on the type of polishing agent and the polishing apparatus. However, the effect of the total amount of the gelled precipitate is similar regardless of which abrasive is used. If the amount of the precipitate exceeds 2% by weight of the total amount of slurry, any abrasive is used. Particles due to polishing were likely to occur. Therefore, it is preferable to control and polish with the amount of precipitate below this. Further, if a slurry adjusted to the pH range of the present invention from the beginning without adding a pH adjuster is used, Na ₂ CO _Three The addition of a pH adjusting agent such as the above is almost unnecessary, or it is not necessary to add to a level that causes a problem even if it is added, and polishing can be performed in a state where a gel-like substance is not generated.
[0045]
In addition, regarding the gelation as in this case, it is considered that there is an influence of the electrical conductivity of the slurry. When the silica concentration is 3% by weight, when the electric conductivity exceeds 13000 μS / cm, the surface of all silica sols has Na ⁺ It was observed that the particle diameter maintained by the repulsive force of the ions could not be maintained due to the adsorption of ions, and a sudden gelation occurred. The state where the electric conductivity exceeds 13000 μS / cm is the state of Experimental Example 5 (Na ₂ CO _Three The concentration was about 2% by weight). It was found that even when the electrical conductivity is controlled to 13000 μS / cm or less, the generation of gel that leads to particles caused by polishing is suppressed, and stable polishing can be performed.
[0046]
Example 1
The wafer polishing apparatus, polishing conditions, and the like are not particularly limited. For example, polishing was performed using a slurry supply circulation type single-side polishing apparatus as shown in FIG. The objects to be polished were subjected to a plurality of batch polishings, with two batches of silicon wafers having a diameter of 300 mm after the primary polishing. The slurry (abrasive) is the same alkaline solution having at least silica as the main component used in Experimental Example 1, and NaOH and Na. ₂ CO _Three The initial pH is adjusted to 10.5 with a pH adjuster comprising A non-woven type polishing cloth (Asker C hardness 80) was used and the polishing pressure was 20 kPa. The polishing allowance at this time was 1.5 μm. These polishing conditions are polishing corresponding to polishing conditions called secondary polishing.
[0047]
In the polishing apparatus and polishing conditions used this time, Na into the slurry ₂ CO _Three It is known that when the amount of addition becomes 2.2% by weight, the gel-like substance (precipitate) becomes about 2.1% by weight. ₂ CO _Three When 2.2 wt% was added, the abrasive was adjusted again and polishing was performed.
[0048]
Actually, although there are some variations, the polishing conditions performed in this example are almost the 27th batch, and the added amount of this concentration is exceeded. Therefore, when the 25th batch is finished, a new polishing agent is used. It was adjusted again. After that, it was adjusted again every 25 batches.
[0049]
As a result, the number of particles of 0.065 μm or more in all wafers was about 0 to 30 and the maximum value was 300 or less. Particles on the wafer were measured with a particle counter [SP1 (DCO mode) manufactured by KLA-Tencor].
[0050]
(Comparative Example 1)
Polishing was performed in the same manner as in Example 1 except that the same slurry was used in the initial state and the same slurry was circulated and used without readjusting the abrasive. Up to the 25th batch, the particles were at the same level as in Example 1, but the subsequent batches were about twice the first 25 batches, for example, 3 to 80 particles with a particle size of 0.065 μm or more. A very large number of particles of 700 or more were sometimes observed. Na ₂ CO _Three It can be seen that the addition of slag causes micro-aggregation of the abrasive, resulting in poor dispersibility, and accompanying this, the number of defects caused by processing increased rapidly.
[0051]
It can be seen that, by controlling the amount of addition of the pH adjusting agent as in the present invention, polishing can be performed while suppressing the generation of particles (defects) due to polishing.
[0052]
The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has substantially the same configuration as the technical idea described in the claims of the present invention, and any device that exhibits the same function and effect is the present invention. It is included in the technical scope of the invention.
[0053]
For example, in the above embodiment, the total amount of the pH adjusting agent added to the slurry is controlled by the number of batches that have been polished, and polishing is performed with feedback such as readjustment of the abrasive after polishing any number of batches. Although an example has been shown, the present invention is not limited to this, and the actual addition amount of the pH adjusting agent may be recorded and managed directly with a flow meter, and the electrical conductivity of the slurry is measured periodically (for example, for each batch). Polishing may be performed by readjusting the abrasive according to the result. The form of the polishing apparatus such as a double-side polishing apparatus or a single-side polishing apparatus is not particularly limited. Further, the wafer may be in the form of a batch type in which a plurality of wafers are polished simultaneously, or a single wafer type in which the wafers are polished one by one.
[0054]
【The invention's effect】
As described above, according to the method of the present invention, it is possible to prevent the occurrence of defects (particles) caused by processing that have appeared after the polishing of the wafer and to produce a mirror surface wafer having an excellent surface state. Is done.
[Brief description of the drawings]
FIG. 1 is a schematic side view showing a polishing apparatus and a slurry supply / circulation system used in the method of the present invention.
FIG. 2 Na in Experimental Examples 1-6 ₂ CO _Three It is a schematic diagram which shows the result of having observed the relationship between the addition amount of and the precipitation amount of a gel-like substance.
FIG. 3 is a schematic side view illustrating an example of a polishing apparatus.
[Explanation of symbols]
30: Polishing surface plate, 33: Work holding plate, 34: Slurry supply pipe, 35: Upper load, 37: Rotating shaft, 38: Rotating shaft, 39: Slurry, 39a: New slurry, 39b: Used slurry, 50 : Slurry supply tank, 52: slurry preparation tank, 54: slurry raw material input pipe, 56: pure water input pipe, 58: pH adjuster input pipe, 60, 74: pH meter, 62: slurry new liquid supply pipe, 64: Slurry recovery tank, 66: drain port, 68: slurry recovery pipe, 70: pump, 72: pH adjuster supply pipe, A: polishing apparatus, B: slurry supply circulation system, D: sediment, M: graduated cylinder, P : Polishing cloth, S: slurry for experiment, W: wafer.

Claims (6)

In a method of holding a wafer on a rotatable wafer holding plate, supplying slurry to an abrasive cloth affixed to a rotatable surface plate, and polishing the wafer surface by sliding the wafer against the abrasive cloth, the slurry is An alkaline solution mainly composed of silica, containing a pH adjuster composed of at least one of Na ₂ CO ₃ and NaOH, and controlling the total amount of the pH adjuster to be added. When the total amount of the slurry reaches a predetermined value, the old slurry is discarded and a new slurry is prepared. Is controlled to 13000 μS / cm or less, and polishing is performed in a state where the slurry has a pH of 10 to 13.   2. The wafer polishing method according to claim 1, wherein the average primary particle diameter of the silica in a dispersed state is 5 nm to 30 nm.   3. The wafer polishing method according to claim 1, wherein the silica concentration in the slurry is 2% by weight to 20% by weight.   The method for polishing a wafer according to any one of claims 1 to 3, wherein a polishing cloth of a non-woven fabric type is used as the polishing cloth.   5. The wafer polishing method according to claim 1, wherein a polishing margin is controlled in a range of 0.5 [mu] m to 2 [mu] m.   6. The wafer polishing method according to claim 1, wherein the slurry is circulated and used.

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